Which of the following statements are not correct? (Note: more than one of the given options may be correct.)

NCERT Exemplar · Q30

Q. Which of the following statements are not correct? (Note: more than one of the given options may be correct.)

(i) NaCl being an ionic compound is a good conductor of electricity in the solid state.

(ii) In canonical structures there is a difference in the arrangement of atoms.

(iii) Hybrid orbitals form stronger bonds than pure orbitals.

(iv) VSEPR Theory can explain the square planar geometry of XeF4.

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Concept understanding — Lewis Dot Structures

Why do we need Lewis dot structures?

Atoms are held together in molecules by chemical bonds — but what exactly is a bond? In the early 20th century, Gilbert N. Lewis realised that the key lies in the valence electrons (the outermost electrons). He noticed that atoms of noble gases (like Ne, Ar) are extremely stable and unreactive, and they all have 8 electrons in their outermost shell (except helium, which has 2). This led to the octet rule: atoms tend to gain, lose, or share electrons to achieve a full outer shell of 8 electrons (or 2 for hydrogen).

Lewis dot structures are simply a shorthand picture of this idea. They show:

Which atoms are connected to which
How many valence electrons each atom contributes
How those electrons are arranged as bonding pairs (shared) or lone pairs (unshared)

The precise statement

A Lewis dot structure (or electron dot structure) represents the valence electrons of an atom or molecule using dots placed around the element's symbol. Each dot stands for one valence electron. Shared pairs (bonds) are shown as lines, and unshared pairs as pairs of dots.

For a single atom, you write the element symbol and place dots on its four sides (top, bottom, left, right) — up to 8 dots. The order of filling doesn't matter for the final picture, but conventionally you place one dot on each side first, then pair them up.

For example:

Carbon (group 14, 4 valence electrons): $\cdot \text{C} \cdot$ (four single dots)
Oxygen (group 16, 6 valence electrons): $\cdot \ddot{\text{O}} \cdot$ (two single dots and two pairs)

How to draw a Lewis structure for a molecule

Here's the step-by-step method you'll use in exams:

Count total valence electrons — add up valence electrons from all atoms. For ions, add 1 electron for each negative charge, subtract 1 for each positive charge.
Identify the central atom — usually the least electronegative element (not hydrogen or fluorine). Place it in the centre.
Connect atoms with single bonds — each bond uses 2 electrons. Subtract these from your total.
Complete octets of outer atoms — place remaining electrons as lone pairs on terminal atoms (except hydrogen, which only needs 2).
Place leftover electrons on the central atom — if any remain.
If the central atom has fewer than 8 electrons, form multiple bonds — move lone pairs from outer atoms to create double or triple bonds until the central atom has an octet.

Watch out

A common mistake: forgetting that hydrogen only needs 2 electrons (a duet), not 8. Never put more than 2 electrons around H.

A concrete example: water (H₂O)

Total valence electrons: O has 6, each H has 1 → $6 + 1 + 1 = 8$ electrons.
Central atom: oxygen (least electronegative after H).
Connect: O—H bonds (2 bonds × 2 electrons = 4 electrons used).
Remaining: $8 - 4 = 4$ electrons → place as two lone pairs on oxygen.
Check: O has 2 bonds (4 electrons) + 2 lone pairs (4 electrons) = 8. Each H has 1 bond (2 electrons) = 2. Done.

The structure: $\text{H} - \ddot{\text{O}} - \text{H}$

What the structure tells you

Once drawn, a Lewis structure reveals:

Bond order (single, double, triple)
Lone pairs (which affect molecular shape and reactivity)
Formal charge (a bookkeeping tool to check which structure is most stable) …

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Statements (A), (B), and (D) are incorrect. NaCl conducts only when molten or dissolved; canonical structures differ only in electron placement, not atomic positions; and VSEPR alone predicts octahedral geometry for XeF₄ — the square planar shape requires invoking hybridization or molecular orbital theory.

The question asks us to identify statements that are not correct, so we need to evaluate each claim against established chemical principles.

Concept: Testing statements against core principles

Each option touches a different area: ionic conductivity, resonance theory, hybridization, and molecular geometry. The key is to recall the precise definitions and limitations of each concept.

Evaluating each statement

1. Statement (A): "NaCl being an ionic compound is a good conductor of electricity in the solid state."

In solid NaCl, the $\text{Na}^+$ and $\text{Cl}^-$ ions are locked in a rigid crystal lattice. They vibrate about fixed positions but cannot move freely through the structure. Electrical conduction requires mobile charge carriers. Only when NaCl is melted (molten state) or dissolved in water do the ions become free to move and carry current.

This statement is incorrect.

2. Statement (B): "In canonical structures there is a difference in the arrangement of atoms."

Canonical structures—more commonly called resonance structures—are different Lewis structures for the same molecule that differ only in the placement of electrons (specifically $\pi$ electrons and lone pairs). The nuclei remain in identical positions. For example, the two resonance structures of benzene show different positions for the double bonds, but all six carbon atoms stay in the same hexagonal arrangement.

If atomic positions changed, we would have different isomers, not resonance structures.

This statement is incorrect.

Watch out

A common mistake is confusing resonance structures (same atomic framework, different electron distribution) with structural isomers (different connectivity of atoms).

3. Statement (C): "Hybrid orbitals form stronger bonds than pure orbitals."

Hybridization mixes atomic orbitals to create new orbitals with directional character that point toward bonding partners. A hybrid orbital like $sp^3$ has greater electron density along the bonding axis than a pure $s$ or $p$ orbital would. This increased overlap with another atom's orbital leads to a stronger, more stable bond.

For instance, carbon uses $sp^3$ hybrids in methane rather than its pure $2s$ and $2p$ orbitals, resulting in four equivalent, strong C–H bonds.

This statement is correct.

4. Statement (D): "VSEPR Theory can explain the square planar geometry of XeF₄."

VSEPR (Valence Shell Electron Pair Repulsion) theory predicts geometry by minimizing repulsion among electron pairs around the central atom. Xenon in XeF₄ has:

4 bonding pairs (to four F atoms)
2 lone pairs
Total: 6 electron pairs …

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Q.Which of the following statements are not correct? (Note: more than one of the given options may be correct.)

Concept: Testing statements against core principles

Evaluating each statement

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